Semiconductor devices are typically formed on a semiconductor substrate and often include multiple levels of patterned and interconnected layers. For example, many semiconductor devices have multiple layers of conductive lines (e.g., interconnects). Conductive lines or other conducting structures, such as gate electrodes, are typically separated by dielectric material (i.e., insulating material) and may be coupled together, as needed, by vias through the dielectric material. The dielectric material may also be used to separate conducting structures, such as conductive lines and gate electrodes, from other conducting structures in the same layer. In addition, dielectric materials may be used in other contexts within the semiconductor device.
The dielectric material typically isolates conducting structures. There is, however, an inherent capacitance formed between conductive lines or other conducting structures separated by dielectric material. This capacitance can negatively impact device properties or parameters including, for example, device speed. Therefore, it is desirable to reduce this capacitance.
Capacitance is a function, at least in part, of the surface area of the conducting structures and the dielectric constant of the dielectric material. Using a dielectric material with a relatively low dielectric constant is one method for reducing the capacitance. One common dielectric material is silicon dioxide, which has a dielectric constant of approximately 3.9. Silicon dioxide can be formed or deposited by a variety of methods, including, for example, thermal oxidation of a silicon layer or substrate and chemical vapor deposition (CVD) using a material such as tetraethyl orthosilicate (TEOS).
Silicon dioxide dielectric materials can also be formed using xerogels, such as spin-on glasses (SOG) including, for example, silicate and siloxane materials. In conventional spin-on glass processing, a silicate or siloxane precursor material is mixed with a solvent and deposited on a device layer of the semiconductor device. The solvent is then evaporated, resulting in a relatively dense dielectric material.
Lower dielectric constants can be achieved by increasing the porosity of the dielectric material. Gases, such as air, within the pores of the dielectric material typically have a much lower dielectric constant than the dielectric material itself. One type of porous dielectric material is a dielectric aerogel formed by supercritical evaporation of a solvent from a solution containing a dielectric material or a precursor material that can be converted into a dielectric material. Conventional silicon dioxide aerogels are formed using a dielectric material or a precursor material, such as TEOS or a spin-on glass. These conventional silicon dioxide aerogels are highly porous materials with dielectric constants ranging from about 1.1 to 2.0 depending on the porosity and structure of the material.
While aerogels do have low dielectric constants, the porosity of aerogels makes these materials fragile. Vias etched through a dielectric aerogel layer often have rough, pitted, anisotropic profiles. For example, the sidewalls of the via may be sloped or bowed. The non-uniformity in the profile of the via results in problems during the subsequent deposition of conducting material. Furthermore, conductive material deposited in the vias may more readily diffuse into the dielectric aerogel layer because of its porosity. In addition, the high surface area and porosity of the dielectric aerogel layer, as well as the hydrophilicity of many conventional aerogels, can lead to degradation of the aerogel and/or conductive material as a result of chemical interaction between the conductive material and the aerogel or compounds, such as water, adsorbed in the aerogel. Therefore, there is a need for new via structures and methods for their production for use with semiconductor devices having dielectric aerogel layers.